What are common symptoms of a failed ILS glide slope?

• A. Improved glide angle.
• B. Glide slope completely unavailable.
• C. Loss of vertical guidance or incorrect glide slope indication.
• D. Horizontal guidance only.

Answer: (C)

Glide slope failure means the vertical guidance the ILS provides is no longer reliable. When the glide slope is working, you have a defined vertical path to the runway; if it fails, you lose that vertical guidance and the system may show incorrect glide slope indications. Practically, you might see the glide slope needle deflect erratically, remain centered while you’re high or low, or display an unreliable/invalid indication. The localizer (horizontal guidance) can still function, so you may still track the lateral course, but the vertical guidance is gone or misleading.

This aligns with common symptoms of GS failure: loss of vertical guidance or incorrect glide slope indication. An option suggesting an improved glide angle isn’t plausible for a failure, and while horizontal guidance only can occur if the glide slope is unusable, the core observable symptom pilots notice is the loss or corruption of the vertical path information.